Thermomagnetic electric relay



March 23,1954 T, CASEY 2,673,263

THERMOMAGNETIC ELECTRIC RELAY Filed May 18, 1951 Z5 7 40 Z8 Z7 Z? /7/ "z 7 His Attowhey.

Patented Mar. 23, 1954 UNITED STATES PATENT OFFICE THERMOMAGNETIC ELECTRIC RELAY Robert T. Casey, Bristol, Comm, assignor, by

mesne assignments, to General Electric Company, a corporation of New York Application May 18, 1951, Serial No. 227,048

9'Claims. 1

My invention relates to improvements in devices or apparatus for controlling electric circuits.

'One object is to provide a current responsive device of simple and economical construction.

Another object is to provide a current responsive device which is responsive to both thermal and magnetic efiects of current.

Another object is to provide a current responsive device of the magnetic type which can be readily adjusted.

In carrying out my invention, I provide separa'ble contacts, holding means for retaining the contacts in closed position, and thermal and magnetic means for causing the release of the holding means at predetermined current values.

Fig. 1 is a side view illustrating one form of my invention, the side cover being omitted and the parts being shown in the closed circuit position.

Figs. 2, 3 and 4 are fragmentary plan views showing the adjustable magnetic control mechanism in high, intermediate and low current positions, respectively.

Fig. 5 is a semi-schematic view of the magnetic circuit involved in the magnetic control.

In Fig. 1, an insulating casing, housing or support I 0 is shown in which is mounted main circuit elements, branch circuit elements and mechanism for controlling the branch circuit. The main circuit terminals H and I2 are supported by the housing and connected by a bimetal strip l3 which is fixed to terminal II at one end and flexibly connected to the other terminal by a flexible conductor M.

A branch circuit has terminals and [5. A stationary contact !"I is connected to the terminal it inside the housing, and a movable contact I8 is carried by one arm of a tilting lever l9 which is pivoted at 23 in the housing. A spring .21 connects under tension one arm of the lever I9 with a fixed abutment 2.2. The other arm 23' of the lever 1 9 is connected by a flexible conductor 25 to the terminal l5. The: action of the spring 2! applies tension to the lever 1-9 tending to open the branch circuit between the contacts I! .and I8. The opening movement, however, is opposed by the insulating abutting member 26 which is carried by the frame 2! pivoted at '28 to the housing. The movable end of the bimetal strip I3 extends through a notch or opening 29 in the member 30 whichis connected to the .frame .part 21.. The spring is biased upwardly against arm 34 of frame 21.

.' When the bimetal member 13 is warped by a 2 gradual low overload in the main circuit, it bears down on the frame member 30 against the bias of spring 35 and retracts the member 26 from the tilting lever 19. The spring then tilts the lever 19 and separates contact [8 from contact I! thus opening the branch circuit.

The branch circuit may be manually closed after such automatic opening by pressing on the plunger member 3! which returns the lever l9 and its contact Hi to closed position, allowing spring 35 to return frame .21 and abutment '25 to latching position when the bimetal l3 has cooled sufficiently.

I have also provided an electro-magnetic system for moving the frame 2'! and automatically opening the circuit, which system coacts with the bimetal strip 13 and includes a ferro-magnetic armature piece or sleeve 32 and the magnet 33. Sleeve 32 encircles the bimetallic member I3 and is secured to it.

Member 33 is a high-strength permanent magnet of a material such as Alnico and has two poles N and S normally in contact with sleeve 32. Magnet 33 is fixedly anchored, such as by soldering, to the head 36 of stem 38. Head 35 is of larger diameter than magnet 33 and provides a base flange which serves as an abutment or seat for a spring 31 which is normally compressed between the armature member 32 and the frame member 34.

The magnet member 33 is rotatable and the stem 38 extends freely through an opening in the frame. member 34.

The action of this magnetic trip is such that on a sudden high overload magnet 33 is released from sleeve 32, permitting spring 3.! to move frame member 38 in a tripping direction against th bias of spring 35. For this purpose, spring 31 is stronger than spring 35.

The magnetic action which causes the release of magnet 33 is considered to be essentially as follows:

When current flows through bimetal l3, its associated magnetic flux will circulate through sleeve 32 as represented by dotted lines in Fig. 5.

At the same time, when magnet 33 is in contact with sleeve 32, its associated magnetic flux will pass through a portion of sleeve 32 as shown by the solid line arrows of Fig. 5.

It will be further understood that the number or density of flux lines due to magnet 33 will dep nd on the strength of-the magnet and the reluctance of the portion of sleeve 32 which these lines pass through. While, technically-speaking. there are many paths which such lines may take through piece 32, the practical operation of the device will be understood by a consideration of the effect on the theoretical flux lines taking the shortest available path as shown.

It is well known that in ferro-magnetic materials magnetic permeability varies with flux density in a predeterminable way. The outstanding characteristic of this variation is that following an initial increase permeability decreases with increased flux density up to a certain point at which the permeability substantially equals that of air.

Applying these consideration to the structure of Fig. 5, it will be seen that as the current in bimetal l3 increases, its associated flux will increase, causing a simultaneous increase in the magnetic permeability of sleeve 32.

Since the amount of flux from magnet 33 depends on the reluctance of sleeve 32, it will be seen that this flux will decrease as the current in bimetal l3 increases. When this flux has decreased to a certain minimum value, the magnetic resultant holding force will decrease to a point where it can no longer overcome the force of spring 31, which will then be free to push the magnet 33 and stem 38 away from bimetal 13, at the same time moving frame member 30 so as to cause release of the contacts as previously described.

The above action, although described in terms of direct current flow, also takes place when alternating current is flowing through bimetal Is. This is thought to be due to the fact that the flux from current in bimetal 13 on a given half cycle materially decreases the holding force of magnet 33, and regardless of What happens on the succeeding half cycle, this momentary decrease is sufiicient to permit the spring 31 to operate. Another theory is that while it is apparent how current on one half cycle can decrease the pull of magnet 33, as explained above, it is not apparent that the current on the succeeding half cycle would equally increase the pull, so that the average holding force of magnet 33 is, therefore reduced.

The efiect of an excess of current in bimetal I3 in causing tripping magnetically as described above may be varied or adjusted, in accordance with my invention, by merely rotating the magnet 33 manually by means of the stem 38. Thus, the effect will be at a maximum (i. e. a lower value of current required to cause release) when the poles of the magnet lie on a line perpendicular to the bimetal strip I3 as in Fig. 4. It will be at a minimum (i. e. a higher value of current required to cause release) when the poles of the magnet lie on a line parallel to the bimetal strip, as in Fig. 2. This is because the saturation eiiect described above exhibits a directional characteristic. By this adjustment, therefore, the magnetic action of the device may be varied independently of the overload characteristics of bimetal strip I3.

While I have shown a construction with terminals for making connections so that current conditions in a first circuit can control contacts in a second circuit, it will be understood that the terminals may be connected so that the contacts are in series with the thermal and magnetic current responsive portion to provide a conventional small "automatic circuit breaker or resettable cut-out. For convenience, all such devices may be termed relays.

I claim:

. 111. In an electrical control device having an element movable upon the occurrence of predetermined electrical conditions in a reference circuit, means for moving said movable element comprising a bimetallic member adapted to be warped by heat generated in said reference circuit, an operative connection between said bimetallic member and said movable element, a magnetic armature member providing a closed magnetic circuit means for causing magnetic flux generated by current in said reference circuit to pass through said armature member along said closed magnetic circuit, a magnet member having pole-faces normally in contact with said magnetic armature said magnet member being arranged to cause magnetic flux to flow in said armature member through a portion of said magnetic circuit in the same direction a said firstnamed flux, means biasing said magnet member away from said armature, and an operative connection between one of said members and said movable element to cause movement of said movable element upon release of said magnet member.

2. In an electrical control device having an element movable upon the occurrence of predetermined electrical conditions in an electric circuit, a magnetic armature member of a material whose reluctance varies directly with density of flux therethrough, said magnetic armature member providing a substantially closed magnetic circuit, means for causing magnetic flux generated by current in said electric circuit to pass through said armature member along said magnetic circuit, a permanent magnet having polefaces normally in contact with a continuous portion of said armature member, means biasing said magnetic armature member and said permanent magnet apart, means for rotatably adjusting said permanent magnet with respect to said armature, and operative connecting means between at least one of said magnetic members and said movable element to cause movement of said movable member upon release of said permanent magnet away from said armature member.

3. In an electrical control device having an element movable upon the occurrence of predetermined electrical conditions in an electric circuit, a magnetic armature member of a material whose reluctance varies directly with density of flux therethrough, said armature member providing a substantially closed magnetic circuit, means for causing magnetic flux generated by current in said electric circuit to pass through said armature member along said magnetic circuit, a rotatably-mounted permanent magnet having polefaces normally in contact with a continuous portion of said armature member, means biasing said magnetic armature member and said permanent magnet apart, a stem projecting from said permanent magnet for rotating said magnet to adjust its position with respect to said armature. and operative means of connection between at least one of said magnetic members and said movable element to cause release of said movable element upon movement of said permanent magnet away from said armature member.

4. In an electrical control device having an element movable upon the occurrence of predetermined electrical conditions in a reference circuit, circuit terminals, means for moving said movable element comprising a current carrying bimetallic strip connected to one of said terminals and adapted to be warped by heat generated in said reference circuit, an operative connection between said bimetallic member and said movable member, a magnetic armature on and substantially surrounding said bimetallic strip, a magnet member having pole-faces normally in contact with a continuous portion of said armature, means biasing said magnet member away from said armature, and an operative connection between said magnet member and said movable element to cause movement of said movable element upon release of said magnet member away from said armature member.

5. In an automatic circuit breaker, a stationary contact, a movable contact, means for biasing said movable contact to open circuit position, an element movable upon the occurrence of predetermined electrical conditions in a reference circuit, said movable element normally holding said biasing means against action, means for moving said movable element comprising a bimetallic member adapted to be warped by heat generated in said reference circuit, an operative connection between said bimetallic member and said movable element, a magnetic armature providing a substantially closed magnetic circuit means for causing magnetic flux generated by current in said reference circuit to pass through said armature member along said circuit, a magnet member having pole-faces normally in contact with said magnetic armature, means biasing said magnet member away from said armature member, and an operative connection between one of said members and said movable element to cause movement of said movable element upon release of said member whereby said biasing means moves said movable contact to open circuit position.

6. In a device responsive to current in an electric circuit, a magnetic armature member made of a material whose reluctance varies directly with density of flux therethrough, said magnetic armature member providing a complete magnetic circuit in itself, means for causing flux associated with current in said electric circuit to flow through said armature member along said circuit in a predetermined direction, a magnet member having pole faces normally in contact with a continuous portion of said armature, means biasing said magnet and said armature apart, supporting and guiding mean providing for rotation of said magnet to a plurality of positions while maintaining its pole faces in contact with said armature, said pole faces having one position in which th flux from said magnet flows through the portion of said armature between said pole faces in said predetermined direction.

7. The invention as described in claim 6 and in which the said magnet has a second position in which the flow of flux from said magnet through the portion of said armature between said pole faces is substantially at right angles to said predetermined direction.

8. In a device responsive to current in an electric circuit, an elongated electrical conductor adapted to be connected in said circuit 0 as to pass said current therethrough, a form-magnetic sleeve surrounding a portion of said conductor and having a flat area on at least one portion of its outer surface, a magnet having its pole faces normally held magnetically in contact with said fiat area of said sleeve, spring means biasing said magnet away from said sleeve, and supporting and guiding means for said magnet including a stem portion attached to and projecting from said magnet, said stem also serving as a means for rotatably adjusting the position of said magnet pole faces on said flat area of said sleeve.

9. In a device responsive to current in an electric circuit, an elongated bimetal having a connection at each end for connection in said electric circuit so as to pass said current there through, a sleeve surrounding a portion of said bimetal and having a flat area on at least one portion of its outer surface, said sleeve being made of a material whose reluctance varies directly with the density of magnetic flux lines therethrough, a permanent magnet having its pole faces normally held magnetically in contact with said flat area of said sleeve, spring means biasing said magnet away from said sleeve, a movable control element, an operative connection between a first part of said movable control element and the outer end of said bimetal, an operative connection between a second part of said movable element and said magnet, said second part being provided with an aperture, and supporting and guiding means for said magnet including a stem portion attached to said magnet and extending through said aperture, said stem also serving as a means for rotatably adjusting said magnet pole faces on said flat area of said sleeve.

ROBERT T. CASEY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re. 15,441 Tritle Aug, 29, 1922 1,248,084 Curtis Nov. 27, 1917 1,687,515 Roberson Oct. 16, 1928 2,004,114 Hubbell, Jr June 11, 1935 2,035,743 Frank et a1 Mar. 31, 1936 2,170,341 Shaw Aug. 22, 1939 FOREIGN PATENTS Number Country Date 211,158 Great Britain Sept. 11, 1924 

